Abstract

An approach of enhanced light-trapping in a thin-film silicon solar cell by adding a two-filling-factor asymmetric binary grating on it is proposed for the wavelength of near-infrared. Such a grating-on-thin-film structure forms a guided-mode resonance notch filter to couple energy diffracted from an incident wave to a leakage mode of the guided layer in the solar cell. The resonance wave coupled between two-filling-factor gratings would laterally extend the optical power and induce multiple bounces within the active layer. The resonance effect traps light in the cell enhancing its absorption probability. A dynamic light-trapping behaviour in solar cells is observed. A photon dwelling time is proposed for the first time to quantify the light-trapping effect. Moreover, the light absorption probability is also quantified. As compared the grating-on-thin-film structure with the one of planar silicon thin film, simulation results reveal that it is 3-fold enhancement in the light absorption within a spectral range of 920–1040 nm. Moreover, such an enhancement can be maintained even the incident angle of near-IR broadband light wave varies up to ±40°.

Time-variant photon numbers corresponding to the wavelength of 1 µm under two incident angles are demonstrated for the planar type and the proposed GMR type of TF-Si solar cells with and without considering material absorption coefficient α.

Time-variant photon numbers corresponding to reflection and transmission of photons in three different interfaces of the planar type and the proposed GMR type of TF-Si solar cells. The insets indicate the locations of monitoring photon numbers.